Method for producing a holding configuration for at least one sheathed optical fiber conductor

ABSTRACT

A method for producing a holding configuration for at least one sheathed optical fiber conductor, which includes forming a holding body with a through-channel having a first channel section expanded over an expansion region into a second channel section opening into an outlet opening having a rounded rim. The method further includes applying a fixing compound from the outlet opening into the expansion region for fixing a section of an optical fiber conductor introduced into the first channel section, dimensioning a width of the first channel section for exerting capillary forces on the fixing compound contributing to filling a gap between the optical fiber conductor and the first channel section, and dimensioning a width of the second channel section for maintaining the fixing compound in the second channel section free of capillary forces, and metering the fixing compound for permitting the optical fiber conductor to emerge through the outlet opening with radial freedom of movement and free of fixing compound.

CROSS-REFERENCE TO RELATED APPLICATION

This is a division of U.S. application Ser. No. 09/067,073, filed Apr.27, 1998 now U.S. Pat. No. 6,249,637, which was a continuation ofInternational Application No. PCT/DE96/02024, filed Oct. 18, 1996, whichdesignated the United States.

BACKGROUND OF THE INVENTION FIELD OF THE INVENTION

The invention relates to a method for producing a holding configurationfor at least one sheathed optical fiber conductor.

Such holding configurations are used, for example, for connecting anoptical fiber conductor end to an electrooptical module, or for couplingto corresponding plug connectors. Holding configurations, as an endpiece which can be coupled, can directly terminate the optical fiberconductor, which is sheathed by a protective sheath, or can surround asection of the optical fiber conductor located in front of the end, sothat the optical fiber conductor runs on both sides of the holdingconfiguration. In each case, the holding configuration has at least oneend (which is called an outlet opening in the following text) of athrough-channel for holding the optical fiber conductor, from which endthe optical fiber conductor emerges.

U.S. Pat. No. 4,984,865 discloses a holding configuration for an opticalfiber conductor which emerges from a cable sheath end together with endsof a strain relief device in the form of strands (aramide fibers). Thecable sheath end is inserted into a plug connector housing, which isfilled with a thermoplastic. It is not possible for unacceptably smallbending radii of the optical fiber conductor to occur in the case ofthat known holding configuration, since the optical fiber conductor iscompletely surrounded by the thermoplastic and runs in a fixed mannerwithin the holding part.

German Patent DE 27 11 670 C2 discloses a holding configuration in theform of a detachable plug connector, in which two optical fibers to becoupled are each bonded by their end region into a centering insert. Thelatter is inserted into one end of a tube, which is used as a guide bodyand can be inserted with the corresponding coupling partner into anadjustment capillary, in order to make contact at the end.

In the case of the holding configuration of the type mentionedinitially, which is known from German Published, Non-Prosecuted PatentApplication DE 43 03 737 A1, corresponding to U.S. Pat. No. 5,574,819, acable end, which has been freed at the end of its cable sheath revealingstrain relief device ends and two optical fiber conductor ends which aresheathed by one protective sheath (buffer) in each case, enters an inletopening of a receptacle. A spreading sleeve is inserted into the cablesheath end and expands the sheath beyond the inlet opening width. Theoptical fiber conductors pass through a through-channel which runs fromthe inlet opening to an outlet opening, and leave the receptacle withradial freedom of movement. The receptacle is partially filled with afixing compound. That surface of the cured fixing compound which isclose to the outlet opening (filling level) is located vertically at adistance below the outlet opening in the longitudinal axis directionwhen the configuration is oriented vertically.

If the cable end, once it has been provided with the holdingconfiguration, is handled incorrectly or carelessly in the rest of theproduction or assembly process, there is a risk of the optical fiberconductors being bent over the comparatively sharp-edged contact line tothe surface of the fixing compound.

That problem is exacerbated if fixing compounds are used which raise upthe optical fiber conductors due to adhesion effects and capillaryforces. Specifically, in practice, it has been found withthrough-channels having a cross section which is dimensioned to be onlyslightly greater than the cross section of the sheathed optical fiberconductor, that the fixing compound, when in the flowing state, rises toan undesirably high extent above the desired filling level due tocapillary effects, and consequently forms sharp edges which lie againstthe optical fiber conductor, closely underneath the outlet opening. Onone hand, if optical fiber conductors are bent beyond their criticalbending radii, they can be irreversibly damaged. Such damage maytemporarily remain concealed by the protective sheath in adisadvantageous manner, and not be detected until final inspection orinitial operation. On the other hand, comparatively narrowthrough-channels are desirable in order to achieve adequate adhesionforces, the necessary amount of fixing compound and its curing time.

In order to overcome that problem, production and assembly have untilnow had to be carried out extraordinarily carefully, with the opticalfiber conductors temporarily being fixed in appropriately constructedproduction holders at least until additional, permanent structuralelements (for example separate kink protection elements) or appropriatehousings with guides were fitted.

SUMMARY OF THE INVENTION

It is accordingly an object of the invention to provide a method forproducing a holding configuration for at least one sheathed opticalfiber conductor, which overcome the hereinafore-mentioned disadvantagesof the heretofore-known devices and methods of this general type andwhich, even immediately after fitting and curing of a fixing compound,and without any additional apparatuses, ensure reliable protection ofthe sheathed optical fiber conductor against unacceptably small bendingradii.

With the foregoing and other objects in view there is provided, inaccordance with the invention, a holding configuration, comprising afixing compound; a receptacle for receiving the fixing compound, thereceptacle having an inlet opening for receiving an end of an opticalfiber cable stripped at the end to expose an optical fiber conductor,and the receptacle having an outlet opening through which the opticalfiber conductor emerges with radial freedom of movement and free of thefixing compound fixing a section of the optical fiber conductor; and aspreading body at least partially inserted into an end of a cable sheathof the optical fiber cable, the spreading body bounding athrough-channel expanded from a first cable section closely surroundingthe optical fiber conductor to a second cable section opening into theoutlet opening, the second cable section having a cross sectiondimensioned relative to a cross section of the optical fiber conductorfor maintaining the fixing compound in the second cable sectionsubstantially free of capillary forces.

While capillary force effects on the fixing compound are achieved in thefirst, narrower section, in order to fix the optical fiber conductorsafely while using little material, as long as the fixing compound isstill a low-viscosity liquid, the deliberate expansion of thethrough-channel results in the capillary effects in the second sectionbeing suppressed in a defined manner. On one hand, the amount of fixingcompound to be introduced can thus be considerably reduced in anadvantageous manner since it is necessary to fill only a comparativelynarrow gap between the optical fiber conductor and the wall of the firstsection. Since, on the other hand, the expansion reliably prevents thefixing compound, which can still flow, from flowing on or risingundesirably in the direction of the outlet opening, the amount of fixingcompound can be dimensioned and introduced without so much care beingrequired in particular with regard to capillary effects. The amount offixing compound is preferably dimensioned in such a way that the opticalfiber conductor remains largely free of fixing compound in the secondsection. In consequence, the optical fiber conductor has radial mobilityeven at the start of the expanded section, and that has a positiveinfluence on the bending geometry, which is governed by the last fixingpoint, close to the outlet opening, of the optical fiber conductor. Theexpansion allows the distance between the fixing point and the outletopening to be set as planned, and to be easily controllable.

The maximum angles or bending radii of the optical fiber conductor whichoccur during the production and assembly processes (without deliberateoverbending) are automatically kept comparatively gentle in conjunctionwith rounding of the rims or edges of the outlet opening which may comeinto contact with the optical fiber conductor. The maximum angle whichcan occur on its own, without deliberate action, between thelongitudinal axis of the holding configuration and the optical fiberconductor is preferably less than 45°.

In accordance with another feature of the invention, the second channelsection expands to approximately twice the width of the first channelsection. This provides a particularly preferred cross-sectional ratio ofthe channel sections.

In accordance with a further feature of the invention, the expansionfrom the first channel section to the second channel section isconstructed like a step, which permits a specially defined control ofthe capillary effects according to a preferred development of theinvention.

In accordance with an added feature of the invention, the spreading bodyhas two essentially parallel webs which extend radially outward as faras the rim of the receptacle and bound the outlet opening. The spreadingmandrel, in combination with the receptacle, forms an outlet openingwith its webs which is specifically constructed for the optical fiberconductor and has a size and contour that can be dimensioned in order toreliably avoid bending radii less than the minimum.

As a supplementary function, the webs according to an advantageousversion of the invention can interact with at least one positioningprojection on the holding part side, which produces a defined positionand secures the spreading body against twisting.

In accordance with still another feature of the invention, the spreadingbody has a shaft.

In accordance with an additional feature of the invention, the narrowchannel section is formed by an axial groove in the spreading body, sothat the optical fiber conductor is guided particularly exactly alongthe spreading body.

In accordance with yet another feature of the invention, a ratio of thediameter of the optical fiber conductor including the sheath, to thewidth of the second channel section and to a distance between theexpansion and the outlet opening, is approximately 1:2:5. This has beenfound to be particularly advantageous with regard to the physicalstructure. In practical tests, with the sheathed optical fiber conductorhaving a diameter of 1 mm, it has been found to be particularlyadvantageous for the distance between the expansion and the outletopening to be at least 5 mm.

With the objects of the invention in view there is also provided amethod for producing a holding configuration for at least one sheathedoptical fiber conductor, which comprises forming a holding body with athrough-channel having a first channel section expanded over anexpansion region into a second channel section opening into an outletopening having a rounded rim; applying a fixing compound from the outletopening into the expansion region for fixing a section of an opticalfiber conductor introduced or to be fitted into the first channelsection; dimensioning a width of the first channel section for exertingcapillary forces on the fixing compound contributing to filling a gapbetween the optical fiber conductor and the first channel section, anddimensioning a width of the second channel section for maintaining thefixing compound in the second channel section free of capillary forces;and metering the fixing compound for permitting the optical fiberconductor to emerge through the outlet opening with radial freedom ofmovement and free of fixing compound.

Other features which are considered as characteristic for the inventionare set forth in the appended claims.

Although the invention is illustrated and described herein as embodiedin a method for producing a holding configuration for at least onesheathed optical fiber conductor, it is nevertheless not intended to belimited to the details shown, since various modifications and structuralchanges may be made therein without departing from the spirit of theinvention and within the scope and range of equivalents of the claims.

The construction and method of operation of the invention, however,together with additional objects and advantages thereof will be bestunderstood from the following description of specific embodiments whenread in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 and 2 are diagrammatic, sectional views of a holdingconfiguration produced by using the method according to the invention;and

FIGS. 3 and 4 are sectional views of a holding configuration accordingto the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the figures of the drawings in detail and first,particularly, to FIGS. 1 and 2 thereof, there is seen a holding orsupport configuration which includes a holding body 1 with an inletopening 2 and an outlet opening 3, between which a through-channel 4runs, in order to hold a section of an optical fiber conductor 5. Theoptical fiber conductor 5 includes an outer protective sheath (“buffer”)6, an inner protective sheath (“coating”) 7 and an optical fiber 8 as asignal conductor, having an exposed end 9 which passes through the inletopening 2. Depending on the application, the holding configuration maybe constructed as a plug connector for coupling to corresponding plugconnector parts or for flange connection to a module housing asillustrated, in which case it is possible in each case to position andfix the end 9 of the optical fiber 8 precisely with the aid of theholding configuration.

The through-channel 4 is divided into at least first and second mutuallyadjacent channel sections 10, 11. The first section 10 is constructed tobe narrower and encloses the protective sheath 6 of the optical fiberconductor 5 except for a narrow gap, which allows the insertion of theoptical fiber conductor, and assists the capillary penetration of afixing compound 12. The second section 11 is expanded considerably incomparison. The curable potting compound or fixing compound 12 which isapplied from the outlet opening 3 surrounds the end of the narrowersection 10 close to the inlet opening and the region of an expansion 14,and fills a gap between the optical fiber conductor 5 and an inner wallsurface of the section 10. The fixing compound 12 is preferably appliedbefore the insertion of the optical fiber conductor, so that when theoptical fiber conductor is inserted, fixing compound also passes into afront region 15 close to the inlet opening, in order to fix the innerprotective sheath 7 and the optical fiber 8.

One aspect that is essential to the invention is that thethrough-channel 4 expands from the narrower first section 10 to thesecond section 11 which is close to the outlet opening. The opticalfiber conductor 5 runs free of fixing compound 12 in the second section11. No capillary forces act on the fixing compound 12 on the outletopening side after the expansion 14 in the section 11. If need be,adhesion forces can lead to the fixing compound being drawn up slightlyon the protective sheath 6 toward the outlet opening 3. Thethrough-channel 4 preferably expands in the second section 11 to a widthW which is at least approximately twice a width w of the first section10. This reliably avoids any capillary effects in the second section 11,so that undesirable wetting and fixing of the optical fiber conductor 5in the second section 11 are reliably prevented. The optical fiberconductor 5 thus has radial freedom of movement in the second section11, in which case, in the event of radial movement, the optical fiber 8is prevented from being kinked or being bent on a radius less than aminimum bending radius 23 at a contact point 18 next to the outletopening, between the optical fiber conductor 5 or its outer protectivesheath 6 and the fixing compound 12.

A rim 20 of the outlet opening 3 which comes into contact with theoptical fiber conductor 5 is rounded, thus reliably preventing bendingradii less than the minimum bending radius in the event of radialmovement of the optical fiber conductor 5. (This consideration ignoresarbitrary, deliberate bending back of the optical fiber conductor overthe rim 20 toward the side having the inlet opening 2). The combinationof the effects of the structure of the through-channel 4 and therounding of the rim 20 ensure that the contact point 18, which iscritical for radial mobility and the bending radii that occur, isconstructed in a controlled manner, that can be predetermined, and is ata sufficient distance 22 from the outlet opening 3, on the inside of theholding body. By preventing capillary effects, the contact point 18cannot become undesirably close to the outlet opening. The position ofthe contact point 18 can be adjusted by the metering of the amount offixing compound, which can be carried out with a considerable amount oftolerance.

The ratio of the width w of the first section 10 to the width W of thesecond section 11 and to a distance 24 between the outlet opening 3 andthe expansion 14 is preferably approximately 1:2:5.

FIGS. 3 and 4 show a holding or support configuration according to theinvention for the preparation of ends of optical cables. This holdingconfiguration includes a receptacle 30 and a spreading body 31, whichcomplement one another to form a holding body 32. One end 33 of anoptical fiber cable 34 enters the receptacle 30. The optical fiber cablehas a cable sheath 35 that is removed at one end, as a result of whichtwo optical fiber conductors 40, 42, which are each surrounded by anindividual protective sheath 36, 37, and ends 43 of a strain-reliefdevice 44 in the form of strands aramide fibers, for example, areexposed, as is seen in FIG. 4. The ends 43 and the end of the cablesheath 35 are potted in an interior 51 of the receptacle 30 with fixingcompound 50, up to a filling level 52.

A spreading mandrel 53 is used to insert the spreading body 31 into theend of the cable sheath 35 until the cable sheath end is expanded beyondthe width of an inlet opening 54 in the receptacle 30 and isconsequently secured from being pulled out axially. Inwardly pointingribs 56, which are raised from the base of the receptacle 30 and reducethe unobstructed width of the receptacle interior, run in the interior51 of the receptacle 30, close to the inlet opening. The end of thecable sheath 35 is additionally supported and is secured againstrotation with respect to the receptacle 30 by interacting with thespreading body 31 and the fixing compound 50. The ribs 56 also allowundisturbed potting, or fixing compound flow, as far as the inletopening 54. The receptacle 30 has a flange attachment 58 through the useof which the holding configuration can be introduced in a manner that isknown per se (German Published, Non-Prosecuted Patent Application DE 4303 737 A1, corresponding to U.S. Pat. No. 5,574,819), and in such a waythat it is protected against twisting, into a duplex connector housing,which dissipates the tensile stresses absorbed by the strain reliefdevice 44. The receptacle 30 and the spreading body 31 are preferablycomposed of transparent material, which allows substances that are curedby light to be used as the fixing compound.

The spreading body 31 has continuous grooves 60, 61 at the sides,running in the axial direction A. The grooves 60, 61 interact with thereceptacle 30 and the cable sheath 35 in each case to form a firstsection 62 of a through-channel 63 for the optical fiber conductors 40,42. The axial grooves 60, 61 each have an expansion step 65, at which awidth w1 of the section 62 (which is matched to the respective opticalfiber conductor cross section) increases by approximately twice to awidth W1, providing a radial boundary of a subsequent, second section66.

The spreading body 31 for each optical fiber conductor has twoessentially parallel webs 70, 71 and 72 (the web which is opposite andparallel to the web 72 cannot be seen due to the representation in thedrawing). The webs extend radially outward to beyond a rim 75 of thereceptacle 30. Each of those edges 76, 77, 78 of the webs which face theoptical fiber conductors 40, 42 are rounded, so that the optical fiberconductors cannot be kinked at sharp edges. The rim 75, a rounded edge79 of the receptacle 30 and the webs 70, 71, 72 together form anindividual outlet opening 80, 81 for each optical fiber conductor. Theaxial grooves 60, 61 in the spreading body 31 interact with the cablesheath 35 to define a respective individual inlet opening 84, 85 foreach optical fiber conductor.

The rim 75 of the receptacle 30 has projections 90, 91 which act aspositioning projections and are constructed as an axial extension. Whenthe spreading mandrel 31 is inserted, the positioning projections 90, 91move between the webs (for example 70, 71) and thus position thespreading body 31 in such a way that it cannot twist. This prevents thecable sheath 35 from being torsioned, and the optical fiber conductors40, 42 from being twisted around one another. In order to make handlingeasier, the spreading body 31 has a shaft 96, along which the axialgrooves 60, 61 continue.

The broadening of the grooves 60 of the expansion step 65 prevents anyfurther rise of the fixing compound 50, due to the capillary effect, inthe axial direction A beyond the expansion toward the outlet openings80, 81 since no capillary forces are exerted on the fixing compound 50in the second section 66 of the through-channel 63 due to the presenceof an adequate gap. While the capillary effect is desirable in order topenetrate the region located underneath the expansion step, forembedding the optical fiber conductors, the strain relief device and thecable sheath, the formation of fixing compound contacts with the opticalfiber conductors above the expansion is deliberately prevented. Adistance α between the outlet openings 80, 81 and the expansion, or thefilling level 52, is preferably dimensioned to be five times the widthw1. A width W2, which is illustrated in FIG. 4 for clarity and is atright angles to the width W1 shown in FIG. 3, is preferably dimensionedin a corresponding manner to the width W1.

In the case of a practical implementation with an optical fiberconductor diameter d of 1 mm, the width W1, which results from thedistance between the webs 70, 71, is preferably dimensioned to be 2 mm.The width w1 is dimensioned to be approximately equal to the opticalfiber conductor diameter, and is thus about 1 mm. The distance α is 5mm.

A resin system which can be activated or cured by light is preferablyused as the fixing compound. Such known resin systems (for example theresin system which can be activated by light and is known by thetrademark KATIOBOND 050 from the company DELO) allow deliberateactivation of the potting compound. Two-component epoxy resins can alsobe used as an alternative.

I claim:
 1. A method for producing a holding configuration for at leastone sheathed optical fiber conductor, which comprises: forming a holdingbody with a through-channel, the through-channel having a first channelsection with a first channel section width, a second channel sectionwith a second channel section width, an expansion region between thefirst channel section and the second channel section, and an outletopening having a rounded rim; applying a fixing compound from the outletopening into the expansion region for fixing a section of an opticalfiber conductor introduced into the first channel section, and meteringthe fixing compound being applied for permitting the optical fiberconductor to emerge through the outlet opening with radial freedom ofmovement and free of fixing compound; and dimensioning the first channelsection width for exerting capillary forces on the fixing compoundcontributing to filling a gap between the optical fiber conductor andthe first channel section with the fixing compound, and dimensioning thesecond channel section width for maintaining the fixing compound in thesecond channel section free of capillary forces.
 2. The method forproducing a holding configuration according to claim 1, wherein the stepof dimensioning the width of the second channel section comprisessetting the width of the second channel section to at least twice awidth of the optical fiber.